According to Reuters, women are more likely to take their birth control pill when they have a longer supply available. For this study, 661 girls and women at a family planning clinic in New York City "received either three-month or seven-month supplies of birth control pills and six months later, 51 percent of the seven-month supply group were still taking the pills, compared to only 35 percent of the group that had fewer pills at a time."

The study, which was published in the journal Obstetrics & Gynecology, didn't examine pregnancy, but earlier this year another study found that women were less likely to have an unplanned pregnancy when they had a longer supply of pills. Out of every 1,000 women who participated, 30 who had one to three-month supplies were pregnant within a year, versus only 10 who had a whole year's supply.